1. INTRODUCTION
Domestic sources of natural gas are not able to keep up with growing demand, causing
supplies of this key energy source to become increasingly dependent on foreign imports as
well the use of natural gas as a source of hydrogen could further aggravate this Situation In
the future. Fossil fuels are limited in this world as well it is polluting atmosphere Due to
pollution many problems generate as global warming. So we should use renewable energy
sources for power generation & other application solar energy represents a huge domestic
energy resource for the, particularly in the Southwest where the deserts have some of the best
solar resource levels in the world. Different technology can be used for using solar energy for
power generation & other application like solar power tower, solar chimney, and
photovoltaic cells. Different types of concentrator are used to concentrate solar energy
parabolic trough is one of them. Parabolic trough concentrates solar radiation at focal point &
can heat up the water inside tube placed at focal point temperature can be raised up to 400°C
which produce steam & that steam can be used in power plants & heating, cooling etc.
1.1 Dying Planet:-
 Fossil fuels are being depleted 10000 times faster than they are formed
 16 million tones of CO2 emitted every 24 hours by human activities
 4ºC rise in global temperature by 2100
 Sea levels could rise by 6m by 2100
 Per Capita Energy Consumption
 Per capita electricity power consumption in India
 Expected rise: 1200 KW-Hours / year by 2012
 3.3 KW energy per day
 80% of world population lies in Developing countries
 40% of worlds total energy consumed by Developing countries
 Worlds Average per capita Energy consumption is equivalent to 2.2 tons0 of coal
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Developed countries per capita consumption is more than 4 to 5 times of average world per
capita consumption & 9 times more than the average per capita consumption of developing
counties.
1.2 Sources of Energy
 Conventional
 Coal
 Oil
 Natural Gas
 Nuclear (Uranium)
Fossil World‟s Reserves India‟s Reserves % of World Remarks on
Fuel (Proven) (Proven) Reserves Indian
Reserves
Coal 984 84,414 8% will last for
b. Tones m. Tones 33 years
Crude 140.4 . 658 0.46% will last for
Oil b. Tones m. Tones 12 years
Natural 144.8 trillion 628 billion cubic 0.43% will last for
Gas cubic meter meters 18 years
India 4th largest producer of CO2
Contribution of CO2 = 1,342,962 metric tons every year
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 Non-Conventional & Renewable
 Wind Energy
 Biomass / Biogases Power
 Small Hydro Power
 Energy from MSW
 Energy from Industrial Waste
 Solar Energy
 Tidal Energy
 Geothermal Energy
1.3 Concept of Renewable Energy
Renewable energy sources are sources that are continuously replenished by natural processes.
For example, solar energy, wind energy, bio-energy - bio-fuels grown sustain ably),
hydropower etc., are some of the examples of renewable energy sources
A renewable energy system converts the energy found in sunlight, wind, falling-water, sea-
waves, geothermal heat, or biomass into a form, we can use such as heat or electricity. Most
of the renewable energy comes either directly or indirectly from sun and wind and can never
be exhausted, and therefore they are called renewable.
However, most of the world's energy sources are derived from conventional sources-fossil
fuels such as coal, oil, and natural gases. These fuels are often termed non-renewable energy
sources. Although, the available quantity of these fuels are extremely large, they are
nevertheless finite and so will in principle „run out‟ at some time in the future
Renewable energy sources are essentially flows of energy, whereas the fossil and nuclear
fuels are, in essence, stocks of energy
So, it is recommended to use renewable energy sources as Solar energy
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2. SOLAR ENERGY
2.1 Why solar energy?
The sun is the most continues and environment friendly source of energy that is provided all
over the world in the most affluent abundance. It is - at present - the only source of energy
that is capable of satisfying the ever increasing energy demand of humankind whose
coverage with conventional energy sources is becoming more and more difficult.
Solar energy is the most readily available and free source of energy since prehistoric times. It is
estimated that solar energy equivalent to over 15,000 times the world's annual commercial energy
consumption reaches the earth every year.
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India receives solar energy in the region of 5 to 7 kWh/m for 300 to 330 days in a year. This
energy is sufficient to set up 20 MW solar power plant per square kilometer land area.
Solar energy can be utilized through two different routes, as solar thermal route and solar electric
(solar photovoltaic) routes. Solar thermal route uses the sun's heat to produce hot water or air,
cook food, drying materials etc. Solar photovoltaic uses sun‟s heat to produce electricity for
lighting home and building, running motors, pumps, electric appliances, and lighting.
The advantages of solar energy systems at a glance:
environmentally friendly systems, active contribution to the conservation of fossil energy
reserves and to the reduction of greenhouse gases, use of the sun as inexhaustible and in
many parts of the globe reliable energy source, very low long-term operation costs
2.2 Solar Thermal Energy Application
In solar thermal route, solar energy can be converted into thermal energy with the help of solar
collectors and receivers known as solar thermal devices. The Solar-Thermal devices can be
classified into three categories:
 Low-Grade Heating Devices - up to the temperature of 100°C. Low-grade solar thermal
devices are used in solar water heaters, air-heaters, solar cookers and solar dryers for domestic
and industrial applications.
 Medium-Grade Heating Devices -up to the temperature of 100°-300°C
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 High-Grade Heating Devices -above temperature of 300°C
2.3 Classification of Solar Power
2.4 Application for solar energy systems
 Hot water generation
 Steam generation
 Heating
 Cooling
 Solar Distillation
 Solar Green House
 Power generation
 Solar Furnace
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3. SOLAR COLLECTORS
The solar collector is the key element in a solar energy system. It is also the novel technology
area that requires new understandings in order to make captured solar energy a viable energy
source for the future.
The function of a solar collector is simple; it intercepts incoming insolation and changes it
into a useable form of energy that can be applied to meet a specific demand. In the following
text, we will develop analytical understandings of flat-plate and concentrating collectors, as
used to provide heat or electricity. Each type is introduced below.
Flat-plate thermal solar collectors are the most commonly used type of solar collector. Their
construction and operation are simple. A large plate of blackened material is oriented in such
a manner that the solar energy that falls on the plate is absorbed and converted to thermal
energy thereby heating the plate. Tubes or ducting are provided to remove heat from the
plate, transferring it to a liquid or gas, and carrying it away to the load. One (or more)
transparent (glass or plastic) plates are often placed in front of the absorber plate to reduce
heat loss to the atmosphere. Likewise, opaque insulation is placed around the backside of the
absorber plate for the same purpose. Operating temperatures up to 125oC are typical.
Flat plate collectors have the advantage of absorbing not only the energy coming directly
from the disc of the sun (beam normal insulation) but also the solar energy that has been
diffused into the sky and that is reflected from the ground.
3.1 Types of Collector
 Photovoltaic cells
 Flat Plate Solar Water Heaters
 Solar Cookers & Oven
 Solar Distillers
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PHOTOVOLTIC CELLS (CPV)
Photovoltaic cells (PV) are used worldwide to convert sunlight into electricity. The PV cell
contains two layers of semiconducting material, one with a positive charge and the other with
a negative charge
When sunlight strikes the cell, some photons are absorbed by semiconductor atoms, freeing
electrons that travel from the negative layer of the cell back to the positive layer, in the
process creating a voltage. The flow of electrons through an external circuit produces
electricity.
Since individual photovoltaic cells produce little power and voltage – they generate only
about one to two watts per cell–they are connected together electrically in series in a
weatherproof module.
To generate even more power and voltage, modules can be connected to one another to form
a solar panel; solar panels are grouped to form an array.
Fig.3.1 Photovoltaic Cell
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FLAT PLATE COLLECTOR
Flat-plate thermal solar collectors are the most commonly used type of solar collector. Their
construction and operation are simple. A large plate of blackened material is oriented in such
a manner that the solar energy that falls on the plate is absorbed and converted to thermal
energy thereby heating the plate.
Tubes or ducting are provided to remove heat from the plate, transferring it to a liquid or
gas, and carrying it away to the load. One (or more) transparent (glass or plastic) plates are
often placed in front of the absorber plate to reduce heat loss to the atmosphere.
Likewise, opaque insulation is placed around the backside of the absorber plate for the same
purpose. Operating temperatures up to 125oC are typical. Flat plate collectors have the
advantage of absorbing not only the energy coming directly from the disc of the sun.
but also the solar energy that has been diffused into the sky and that is reflected from the
ground.
Flat plate thermal collectors are seldom tracked to follow the sun's daily path across the sky,
however their fixed mounting usually provides a tilt toward the south to minimize the angle
between the sun's rays and the surface at noontime. Tilting flat-plate collectors toward the
south provides a higher rate of energy at noontime and more total energy over the entire day
Fig.3.2 Solar water heating Process using Flat plate collector
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Solar Water heating
Solar energy Passive & active heating
Passive system:
Absorbs & stores heat from the sun directly within a structure
Active system:
Collectors absorb solar energy, a pump supplies part of a buildings heating or water heating
needs.
Fig.3.3 PASSIVE & ACTIVE HEATING
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Solar cookers & Oven
Solar cookers or ovens are primarily used in developing nations as a primary method for
cooking using passive solar heat to cook primary meals
The basic principles of all solar cookers are:
Concentrating sunlight: Some device, usually a mirror or some type of reflective metal, is
used to concentrate light and heat from the sun into a small cooking area, making the energy
more concentrated and therefore more potent.
Converting light to heat: Any black on the inside of a solar cooker, as well as certain
materials for pots, will improve the effectiveness of turning light into heat. A black pan will
absorb almost all of the sun's light and turn it into heat, substantially improving the
effectiveness of the cooker. Also, the better a pan conducts heat, the faster the oven will
work.
Trapping heat: Isolating the air inside the cooker from the air outside the cooker makes an
important difference. Using a clear solid, like a plastic bag or a glass cover, will allow light
to enter, but once the light is absorbed and converted to heat, a plastic bag or glass cover will
trap the heat inside. This makes it possible to reach similar temperatures on cold and windy
days as on hot days.
Insulated box that collects solar radiation enhanced by reflectors attached to each side
Fig.3.4 Solar cookers & Oven
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Solar Distillers
We can use solar energy to distillate sea water in to drinking water.
Solar radiation heats up the contaminated water and allows the water to evaporate, leaving
the contaminant behind
System design collects distilled water for use. Technology purifies water and can serve from
one person to a community depending on the size of system installed
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4. CONCENTRATING SOLAR POWER
Concentrating solar power (CSP) is a renewable generation technology that uses mirrors or
lenses to concentrate the sun‟s rays to heat a fluid, e.g., water, which produces steam to drive
turbines. CSP differs from solar photovoltaic (PV) technology, which directly converts the
sun‟s ultraviolet radiation to electricity using semiconductors.
The CSP technologies discussed here are utility scale although some rooftop CSP
applications are being developed. Solar PV rooftop applications are common; however,
utility-scale solar PV is also being deployed. Because no input fuel is required, CSP plants
Release little or no carbon dioxide equivalent (CO2e) emissions. CSP is a proven technology
with more than 350 megawatts (MW) of installed capacity operating commercially in the
Mojave Desert since the 1980s and several smaller new plants brought on line since 2006.
The current worldwide installed capacity is more than 500 MW, relying mostly on the
established line-focusing parabolic trough technology that provides peak demand generation.
Several emerging technologies that promise higher conversion efficiencies and cost-
competitive generation have been demonstrated on a smaller scale. These technologies, such
as point-focusing power towers and line-focusing Fresnel reflectors, may extend the ability
of CSP to provide shoulder or base load power in addition to peak load. There is a vast
abundance of solar resources and qualified land for deployment of CSP.
Concentrating solar collectors have either a highly reflective surface or multiple Fresnel lens.
Built up as a parabolic dish, or a trough. Both gadgets are made with reflective surfaces.
The Parabolic dish focuses sunlight into a concentrated area, usually an absorbent pipe where
heat gets absorbed by some kind of liquid.
The absorber is always much smaller that the reflector otherwise it would block the sun‟s
light. This way, sun‟s energy is highly concentrated into a small space.
The trough does the same thing as the dish, except the trough directs sun light on a focal
point along the concentrator‟s entire length.
Solar energy is absorbed, transformed, and concentrated in a solar thermal collector over a
time or spatial gradient to produce usable energy
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5. TYPES OF CONCENTRATOR
 Dish stirling (Parabolic Dish)
 Solar Power Tower
 Solar Chimney
 Linear Concentrator
• Fresnel Reflector
• Parabolic Trough
Fig 5.1 Concentrators
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5.1 Dish Stirling (Parabolic Dish)
So-called Dish–Stirling systems can be used to generate electricity in the kilowatts range.
A parabolic concave mirror (the dish) concentrates sunlight; the two-axis tracked mirror must
follow the sun with a high degree of accuracy in order to achieve high efficiencies. In the
focus is a receiver which is heated up to 650°C.
The absorbed heat drives a Stirling motor, which converts the heat into motive energy and
drives a generator to produce electricity.
If sufficient sunlight is not available, combustion heat from either fossil fuels or biofuels can
also drive the Stirling engine and generate electricity. The system efficiency of Dish–Stirling
systems can reach 20% or more.
Some Dish–Stirling system prototypes have been successfully tested in a number of
countries.However, the electricity generation costs of these systems are much higher than
those for trough or tower power plants, and only series production can achieve further
significant cost reductions for Dish–Stirling systems.
Fig.5.2 Dish-Stirling prototype systems
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5.2 Solar Power tower
Power tower” systems use a field of hundreds to thousands of mirrors (heliostats) that
individually track the sun along two axes and focus sunlight on a central receiver placed at
the top of a tower. Because of the high concentration of solar energy, operating temperatures
can range much higher than in trough or LFR systems, 450°C to 550°C and above, which
enables higher operating efficiencies in the Rankine cycle. The higher operating temperatures
also allow molten-salt heat-transfer and storage capabilities, so the plants can deliver
electricity during cloudy periods or at night.
A solar power tower or central receiver generates electricity from sunlight by focusing
concentrated solar energy on a tower-mounted heat exchanger (receiver). This system uses
hundreds to thousands of flat sun-tracking mirrors called heliostats to reflect and concentrate
the sun's energy onto a central receiver tower. The energy can be concentrated as much as
1,500 times that of the energy coming in from the sun.
Energy losses from thermal-energy transport are minimized as solar energy is being directly
transferred by reflection from the heliostats to a single receiver, rather than being moved
through a transfer medium to one central location, as with parabolic troughs.
Power towers must be large to be economical. This is a promising technology for large-scale
grid-connected power plants. Though power towers are in the early stages of development
compared with parabolic trough technology, a number of test facilities have been constructed
around the world
Fig.5.3 Solar Power Tower
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5.3 Solar Chimney
The solar chimney power plant converts global irradiance into electricity. Since chimneys are
often associated negatively with exhaust gases, this concept is also known as the solar power
tower plant, although it is totally different from the tower concepts described above. A solar
chimney power plant has a high chimney (tower), with a height of up to 1000 meters, and
this is surrounded by a large collector roof, up to 130 meters in diameter, that consists of
glass or resistive plastic supported on a framework (see artist‟s impression).Towards its
centre, the roof curves upwards to join the chimney, creating a funnel.
The sun heats up the ground and the air underneath the collector roof, and the heated air
follows the upward incline of the roof until it reaches the chimney. There, it flows at high
speed through the chimney and drives wind generators at its bottom. The ground under the
collector roof behaves as a storage medium, and can even heat up the air for a significant
time after sunset. The efficiency of the solar chimney power plant is below 2%, and depends
mainly on the height of the tower, and so these power plants can only be constructed on land
which is very cheap or free. Such areas are usually situated in desert regions.
However, the whole power plant is not without other uses, as the outer area under the
collector roof can also be utilized as a greenhouse for agricultural purposes. As with trough
and tower plants, the minimum economical size of solar chimney power plants is also in the
multi-megawatt range.
Fig.5.4 Solar Chimney
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5.4 Linear Concentrator
Fresnel Reflector Systems
A second linear concentrator technology is the linear Fresnel reflector system. Flat or slightly
curved mirrors mounted on trackers on the ground are configured to reflect sunlight onto a
receiver tube fixed in space above these mirrors.
A small parabolic mirror is sometimes added atop the receiver to further focus the sunlight.
Fig.5.5 Fresnel Reflector
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Parabolic Trough
The Parabolic Trough Collector is producing steam from solar radiation, which is used for:
heating, cooling, freezing, seawater desalination and/or power generation.
A parabolic trough is a large, curved mirror that sits on a motorized base, allowing it to
follow the movement of the sun throughout the day. The mirror's unique parabolic shape is
designed to gather a great deal of sunlight and then reflect that light onto a single point,
concentrating the solar power.
Lightweight, stiff and precise parabolic reflector panels manufactured from composite
(reinforced polymeric) materials
Concept of Parabolic Trough
It is a principle of geometry that a parabolic reflector pointed at the sun will reflect parallel
rays of light to a focal point of the parabola. A parabolic trough is a one-dimensional
parabola that focuses solar energy onto a line. Physically, this line is a pipe with flowing
liquid inside that absorbs the heat transmitted through the pipe wall and delivers it to the
thermal load.
A trough captures sunlight over a large aperture area and concentrates this energy onto a
much smaller receiver area, concentrating the intensity of the sun.
The concentration ratios, which are the amount of solar energy on a receiver with a reflector
divided by the amount that would normally be on the receiver, range between 30 and 80.
It is the process of concentration that allows troughs to deliver high temperature thermal
energy. In order to achieve the desired concentration, a trough tracks the sun in one axis
continually throughout the day. The required tracking accuracy is within a fraction of a
degree.
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Material used for Parabolic Trough
• Polished aluminum
• Thick mirrored glass
• Thin mirrored glass
• Silverized polymer film on Al
Design Consideration
To reduce the heat loss due to convection and conduction, the space between absorber and
cover is evacuated. The absorber is painted with high absorptance paint. Cover material is
selected to have high transmittance. A reflective coating is also applied on the inside of the
cover to reflect the radiation back onto the absorber.
For good result & Concentration Parabolic Trough should have following characteristics:
• High optical and tracking accuracy
• Low heat losses
• Manufacturing simplicity
• Reduced weight and cost
• Increased torsional and bending stiffness under wind loads
• Reduced number of parts
• Corrosion resistance
• More compact transport methods
• Reduced field erection costs, w/o loss of optical accuracy
• Increased aperture area per SCA (reduced drive, control and power requirements per unit
reflector area)
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Finding the Focal Point
The focal point is the point at which light waves traveling parallel to the axis of the parabola
meet after reflecting off its surface.
If you decide to build a parabolic Trough, you will need to find the focal point of your
Trough in order to place your fluid Absorber Tube where the sun‟s rays will be strongest.
As light rays hit a parabolic reflective surface, they reflect at an angle that directs them to the
focal point of the parabola. Solar energy is focused to a point but only for one specific angle;
hence it needs to be rotated to track the sun.
The formula of focal point for a parabola is
F = x²/4a Where F = Focal Point
x = Radius of the curve
a = Depth of Parabola
F =Focal point = A point located ½ the distance of arc‟s radius
Fig.5.6 Sun Rays Reflected to Focal point
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Modeling Collector
Heat gained by the absorber is given by:
Qu = (It x No x Ac) - (heat loss from the collector)
Where,
It= beam radiation depends on type of tracking used.
No=optical efficiency depends on mirror reflectance, transmittance of cover, absorptance of
receiver etc.
Ac=collector area
Major heat loss is by radiation as the other forms of heat transfer are negligible and are
eliminated to some extent using proper design.
Fig.5.7 Concentration at focal Point of Parabolic trough
A receiver tube sits at the point where the mirror concentrates all the sunlight. The tube is
filled with synthetic heat transfer oil, heated by the mirror's light to around 750 F (400 C).
This superheated oil is then pumped from the solar field to a nearby power block, where the
oil's heat is converted to high-pressure steam in a series of heat exchangers. This steam
pushes a conventional steam turbine, creating electricity.
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6. PARABOLIC TROUGH POWER PLANTS
6.1 Working Principle
Parabolic trough Power plants basically working on Rankine cycle
Working is same as other thermal power plants but in this type of power plants the steam is
produced by concentrating sun rays in parabolic trough.
6.1 Rankine Cycle
The solar field of a parabolic trough power plant is comprised of many rows of parabolic
troughs around six meters high and several hundred meters long. Despite their enormous
size, these high-precision optical devices are aligned with millimeter precision.
The rows run in a north-south direction and track the sun from east to west during the course
of the day.Special components are used for the collectors. The concave mirrors are made
from silver-coated white glass which is about 4 to 5 mm thick and 2 to 2.8 square meters in
size. Over 98% of the solar radiation that arrives at the mirrors is reflected onto the absorber
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pipe along the focal line of the collectors. The absorber pipes contain a heat transfer medium
which is heated to around 400 °C by the concentrated sunlight.
The absorber pipes, also known as receivers, consist of a metal pipe which contains the heat
transfer medium, surrounded by a glass pipe. Between the two pipes is a vacuum which
insulates the metal pipe, thus reducing heat loss. The glass pipe is composed of special
materials and coatings to enable as much solar radiation as possible passing through to be
absorbed by the metal pipe rather than being reflected.
Fig.6.2 Cycle of Power Plant
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6.2 The main components of parabolic trough technology
Basic Components
 Trough Collectors (single axis tracking)
 Heat-Collection Elements
 Reflectors
 Drives, controls, pylons
 Heat-transfer Oil
 Oil-to-water Steam Generator
 Oil-to-salt Thermal Storage
 Turbine-Generator
 Conventional Rankine Cycle Power block
Collector Field consists of:
 PolyTrough modules combined to form the required field size
 Pumps, valves and field reticulation
A collector field master controller and field wiring, assuring fully automatic and safe
operation and communication with the building or process control system
Buffer storage and associated equipment (optional)
Fig.6.3 Concentrator
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Fig. 6.4 Operating Scheme for parabolic trough technology
The parabolic trough reflector : The cylindrical parabolic reflector reflects incident
sunlight from its surface onto the receiver at the focal point. Typically, the reflector is made
of thick glass silver mirrors formed into the shape of a parabola. Alternatively, mirrors can be
made from thin glass, plastic films or polished metals.
Fig.6.5 Reflector
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The receiver tube or heat collection element: The receiver tube consists of a metal
absorber surrounded by a glass envelope. The absorber is coated with a selective coating to
maximize energy collection and to minimize heat loss. The glass envelope is used to insulate
the absorber from heat loss, and is typically coated with an anti-reflective surface to increase
the transmittance of light through the glass to the absorber. For high temperature CSP
applications, the space between the absorber and glass tube is evacuated to form a vacuum.
Fig.6.6 Absorber Tube
The sun tracking system: An electronic control system and associated mechanical
drive system is used to focus the reflector onto the sun.
Fig. 6.7 sun tracking system
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Tracking the sun from east in the morning to west in the evening will increase the efficiency
of the solar panel by 20-62% depending on whom you ask and where you are in the world.
Near to equator, you will have the highest benefit of tracking the sun.
The basic functional blocks of this system are six sensors and their operation depends upon
the intensity of light falling on solar panel. All sensors (each with different functionality)
send their output to microcontroller AT89c52.Then the microcontroller executes predefined
task in its software.
Automatic Tracking System include following:
 Senses all of six sensors.
 Drives stepper motor.
 Drives LCD.
 Controls the warning indicators e.g. buzzer, LED‟s etc.
 Communicates (by parallel port) with the slave microcontroller.
The support structure: Typically made of metal, the collector support structure holds
the mirrors in accurate alignment while resisting the effects of the wind.
Fig .6.8 parabolic trough power Plant
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Fig.6.9 Comparison of flat plate & parabolic Trough collector Power plants
6.3 Comparison of flat plate & parabolic Trough collector
Flat plate collectors or evacuated tubes are designed for residential water and space heating
applications, but they are not well suited for large-scale commercial and industrial
applications. The reasons why troughs are more appropriate are:
Operating Temperature and Efficiency:
Flat plate collectors have a large absorber surface from which to lose heat and hence their
performance rapidly degrades as operating temperatures rise. The practical limit for the
efficient delivery of energy is in the range of 140 – 160 F (60 – 70 C).Evacuated tubes are
generally non-concentrating or only slightly so, and similarly have a large area for heat loss.
A vacuum is designed to limit conductive and convective heat loss so they have a slightly
higher practical limit for thermal energy delivery compared to flat plates. However, on loss
of vacuum, they perform much worse than a flat plate.
A parabolic trough only uses the direct component of solar radiation, whereas non-
concentrating collectors can absorb the direct and diffuse component of solar radiation.
However, because troughs track, in good solar areas, even taking out the diffuse component,
they intercept more solar energy.
Abengoa troughs concentrate solar energy about 40 times onto a small area of absorber tube.
Thus, there is only a small area for heat loss. This allows troughs to operate with good
efficiency even when delivering energy at temperatures up to 260 C. At temperatures around
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100 C, which is about the upper limit for evacuated tubes and essentially beyond the
capabilities of flat plates, troughs will be operating at efficiencies better than 60% in
converting solar energy into useful heat.
Energy delivery:
Because troughs intercept more energy in good solar areas, and because they operate at a
higher efficiency (except for the lowest of temperatures, such as heating a swimming pool),
they deliver much more energy than flat plates or evacuated tubes. They can also deliver
energy over a longer time period. For instance, in the summer the sun will rise and set to the
north (in the northern hemisphere).Flat plates and evacuated tubes are mounted tilted to the
south. Hence, they will not start collecting energy until late in the morning when the sun
illuminates their surface. In contrast, a trough tracks to face the sun early and late in the day
and therefore delivers energy for a much longer period during the day. This can be important
when trying to meet loads not in the middle daylight hours, such as cooling loads that peak in
late afternoon.
Ease of design:
It is much easier to design large parabolic trough fields than flat plate or evacuated tube
systems. This is because a single flow path of a trough field removes heat from a large area
of collectors. In contrast, the area of flow paths for non-tracking collectors is very small.
Thus, you have many, many parallel flow paths. In addition, within each flow path there are
tens of individual flow paths or risers in parallel. It is a major challenge to maintain equal
flows throughout flat plate and evacuated tube collector fields. Usually, some type of
balancing valve is employed or reverse return piping is employed. All of these solutions
increase cost and complexity, while reducing thermal output. Nevertheless, they are
necessary since the penalty for failure is large. Collectors that do not receive adequate flow
will operate with poor efficiency.
Reduced complexity, cost of balance of plant and running costs:
Parabolic trough collector efficiency is much less affected by operating temperature than
non-tracking collectors. Hence, Abengoa Solar parabolic troughs typically operate at
differential temperatures across the solar field that are a number of times greater than the
differentials across non-tracking flat plates or evacuated tubes. This means that flow rates for
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non-tracking collectors are correspondingly larger and piping and pumps are larger and more
expensive. These differences result in increased heat loss, slower startup up and increased
electricity consumption. Other components in a trough system, such as heat exchangers are
also less expensive because of the great temperature driving force and energy storage tanks
can be smaller since they can be efficiently heated to higher temperatures.
Installed cost:
Parabolic trough collectors use much less materials than non-tracking collectors. Added to
lower balance of plant costs and the use of steel for piping compared to copper in flat plates
and evacuated tubes, the installed cost of parabolic trough collector fields is much less than
these less satisfactory alternatives.
Ease of maintenance:
The fact that a trough moves is considered a major disadvantage, in terms of complication,
compared to non-tracking collectors. While tracking is an added complexity, drive and
control systems are so reliable and require so little maintenance as to outweigh the
disadvantages of not tracking. For instance, if needed for maintenance, a trough can be de-
focused. The collector and the heat transfer fluid cools down so that systems can be worked
on. However, it is not possible to “turnoff” a non-tracking system and they remain hot in the
presence of sunlight. In fact any reduction in flow can cause major problems. Temperatures
in flat plates under no-flow or stagnation conditions rise to over 300 F. This is far beyond the
operating temperature and can degrade the collectors and the collector fluid. System
pressures rise, temperatures approach the melting point of solder and leaks can develop.
Evacuated tubes stagnate at very high temperatures to the point where the vacuum can be
compromised and they are rendered useless for energy collection.
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6.4 Current Status
The largest solar electric generating plant in the world produces a maximum of 354
megawatts (MW) of electricity and is located at Kramer Junction, California. This solar
energy generating facility, shown below, produces electricity for the Southern California
Edison power grid supplying the greater Los Angeles area. The authors' goal is to provide the
necessary information to design such systems.
The solar collectors concentrate sunlight to heat a heat transfer fluid to a high temperature.
The hot heat transfer fluid is then used to generate steam that drives the power conversion
subsystem, producing electricity. Thermal energy storage provides heat for operation during
periods without adequate sunshine.
Fig.6.10 Solar electric energy generating systems at Kramer Junction, California, with
a total output of 354MWe.
FPL Energy – Florida
Florida Power and Light have been involved with the original Luz plants as mentioned
above. Apart from Kramer Junction, they currently have ownership of the remaining assets of
these original installations totaling 150MW.
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The parabolic trough design has been proven to be reliable and long lasting and FPL have
contracted to build 250MW in addition to what they currently own and operate. There are
expansion plans to build 850MW generation by 2015.
Today, see the 64 mW (64,000 kW) plant installed in Boulder City, Nevada (Nevada Solar
One). In the case of Solar One (above) a solar powered steam turbine generator provides
enough electricity to Nevada Power Company for 14,000 households.
Fig 6.11 64 mW (64,000 kW) plant installed in Boulder City, Nevada (Nevada Solar
One).
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7. ADVANTAGES & DISADVANTAGE
OF SOLAR THERMAL POWER PLANTS
ADVANTAGES
 Parabolic trough power plants are suitable for large-scale use in the range of 10 to
200 MW electrical output. The modular character of the solar field makes it possible to
start at any power level. Currently the optimal size is 150 - 200 MW. Parabolic trough
power plants can re-place conventional thermal power plants - and without any
qualitative changes in the grid structure.
 Due to the option of thermal storage, the turbines of solar thermal power plants
can also produce power in low-radiation periods and at night. Solar thermal power
plants can deliver power reliably, on a planned schedule, and in a way that keeps the
grids stable.
 Solar thermal power generation can be combined with conventional thermal power
plants. Combined utilization leads to substantial cost reductions and thus facilitates entry
into the use of renewable energies, particularly for threshold countries.
 The use of solar energy means reliable planning. The independence of the operating
costs from fluctuating fuel prices and unlimited availability permit reliable calculation
throughout the entire investment period.
 Particularly in the sunbelt where most power is needed for cooling, solar thermal
power plant technology is most effective. These power peaks are already covered
competitively today by the nine solar thermal power plants in California.
 Solar thermal power plants use low-cost, recyclable materials that are available
worldwide: steel, glass, and concrete. Local companies handle a great share of the
construction work. The modular structure of the solar field facilitates entry into mass
production with substantial potential for increased efficiency.
 Solar thermal power plants have a very good ecological balance. The energy payback
time of five months is low even in comparison to other regenerative energies.
Parabolic trough technology has the lowest material requirements of all solar thermal
power plant technologies.
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 The land use of solar thermal power plants is substantially lower than for biomass,
wind energy, or water power not to mention dams in mountains. In addition, since
they are erected only in the dry zones of the Earth, there is hardly any competition for
land utilization. Solar thermal power plants can be used in the Earth's sunbelt between 35°
northern and southern latitude.
 The waste heat of solar thermal power plants can be used for sea water desalination, as
well as for electricity generation.
DISADVANTAGES
 Diffuse source you need large number of solar panels to produce the needed electricity,
from there you need a large land spot for this purpose
 Large land area required for establish a Solar power plants & generating electricity
 There are locations in the world where this energy is collected efficiently. But some of the
locations are not with the appropriate sunlight.
 The initial cost of the solar power plants are expensive investment
 You can collect it only during the day
 Depends on the climate conditions
 More maintenance is required.
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8. Typical Applications
Pressurized water or thermal oil is pumped through the field and is heated by the
concentrated solar radiation to the required temperature. A buffer storage absorbs short term
fluctuations of the solar radiation. The
Solar heat can be used for solar air conditioning, industrial process heat, electricity
generation, sea water desalination or other mid-temperature applications.
Process heat
Solar heat at up to 220 °C is delivered into the industrial process heat system. The solar heat
serves as a fuel saver by replacing conventional fossil fuels whenever the sun shines.
Many industrial plants are suitable to accommodate solar process heat systems, for example
in food processing (dairy, breweries, meat processing), textile or chemicals.ith the current
high fossil energy prices, solar process heat is becoming a viable option in the sun belt
regions
Fig.8.1 Process heat
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Solar cooling
Solar heat drives a high efficiency absorption chiller to deliver chilled water for air
conditioning or other cooling applications.
The high temperature from the collector allows the use of more efficient chillers and results
in lower cost per kWh cold than systems with flat plate or CPC collectors.
Solar cooling is a perfect match of demand for air conditioning and solar resource. This
makes it a particularly interesting solution in regions with air conditioning driven summer
Electricity peaks.100% availability can be achieved with a combination of storage and a
back-up source (either a conventional electrically driven chiller or an alternative heat source).
Multi-Generation
The use of the solar heat is maximized by cascading applications at different temperature
levels. The 220°C solar heat drives an Organic Rankine Cycle (ORC turbine) to generate
electricity.
An absorption chiller next uses the heat at 165°C for cold production. The remaining
temperature level can be used for hot water production and space heating.
Other combinations are possible, e.g. production of high quality drinking water with a solar-
driven flash desalination system.
Fig 8.2 Solar cooling & multi-Generation
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9. CONCLUSION
Sun: Energy source for the Future. Solar Concentrators economically viable. Solar One Just
the Beginning. Solar Thermal Industry profitable in near future.
Solar energy can be used easily & effectively in place of conventional energy sources. Which
are environmentally friendly systems, active contribution to the conservation of fossil energy
reserves and to the reduction of Pollution in atmosphere greenhouse gases, & global warming
etc.
Conventional Power plants required less land area. Whereas Non-conventional Power plants
required more land area
Conventional Power plants running costs are more. Whereas solar thermal plants running
cost are less.
Conventional Power plants installation cost is less Where as Solar thermal plants installation
cost are more.
There are Different technology are in progress for better efficiency & reduction in cost for
solar thermal power plants. Like parabolic trough technology. We can reduce the cost of
parabolic power plants & can increase efficiency by using better material for mirrors, by
using sun tracking system & distinctly improved optical key values for selective
absorber tube coating, abrasion-resistant anti-reflective coating, if needed greater
absorber diameter to capture lost radiation. & by improving the design of parabolic trough
It is much easier to design large parabolic trough fields than flat plate or evacuated tube
systems. Parabolic trough collector efficiency is much less affected by operating temperature.
Solar systems are required continuously solar energy & also big land area therefore it is not
suitable everywhere, also installation & maintenance cost is higher of solar power plants.
Mostly Suitable in desert area.
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10. REFERNCE
www.abengosolar.com
www.esolar.com
www.solitem.org
www.solarmillenium.com
www.nrel.gov
www.csptoday.com
www.sciencedirectory.com
Book:
“Non-Conventional Energy Sources” by G.D Rai
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